Solve small string and API tasks
Company: NVIDIA
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Onsite
You are given three small programming tasks (typical “easy” difficulty). Implement each as a function.
## Task 1: Validate parentheses
Given a string `s` consisting only of the characters `'(' , ')' , '{' , '}' , '[' , ']'`, determine whether it is valid.
A string is valid if:
- Open brackets are closed by the same type of brackets.
- Open brackets are closed in the correct order.
- Every close bracket has a corresponding open bracket.
**Input:** `s` (length `0…1e5`)
**Output:** `true` if valid, else `false`
## Task 2: Longest substring without repeating characters
Given a string `s` (ASCII), return the length of the longest substring that contains no repeated characters.
**Input:** `s` (length `0…2e5`)
**Output:** integer length
## Task 3: Fetch from a public GET API and transform
You are given a public HTTP GET endpoint that returns JSON.
Assume the endpoint returns an array of records in the form:
```json
[
{"id":"a1","group":"books","amount":12,"ts":"2026-01-01T10:00:00Z"},
{"id":"a2","group":"books","amount":7,"ts":"2026-01-01T11:00:00Z"},
{"id":"b1","group":"games","amount":20,"ts":"2026-01-02T09:00:00Z"}
]
```
Write code that:
1. Calls the endpoint.
2. Parses the JSON.
3. Produces a summary per `group` with:
- `count` of records
- `totalAmount` (sum of `amount`)
4. Returns the summary list sorted by `group` ascending.
**Constraints/notes:**
- Records may be empty.
- `amount` is a non-negative integer.
- You may assume the response fits in memory (≤ `1e5` records).
- Focus on correctness and clean error handling (HTTP errors, invalid JSON).
Quick Answer: This question evaluates proficiency in string algorithms (bracket validation and longest non-repeating substring) and practical API skills including HTTP request handling, JSON parsing, and data aggregation.